As a method for producing methacrolein and/or methacrylic acid using isobutylene or tertiary butylalcohol (hereinafter, referred to as tertiary butanol) as a raw material by fixed-bed catalytic gas phase oxidation reaction is already well known, various complex oxide catalysts for it have been proposed. Among them, a method using tertiary butanol (hereinafter, also referred to as t-butanol), which is in a liquid state at ordinary- temperatures, as a raw material costs lower than using isobutylene which is in a gas state at ordinary temperatures, and is frequently used as a raw material. A production process of methacrolein and/or methacrylic acid using t-butanol as a raw material will be illustrated as follows.
(1) First of all, t-butanol is heated to no lower than its boiling point for vaporization, which is then mixed with a gas containing at least oxygen to obtain a raw material mixed gas, otherwise t-butanol in a liquid state is, for example, atomized and then mixed with a gas containing at least oxygen, and then said mixture is heated to no lower than the boiling point of t-butanol for vaporization of the t-butanol to obtain a raw material mixed gas.
(2) Subsequently, the resulting mixed gas (a raw material gas) is passed through a dehydration catalyst to decompose part of t-butanol into isobutylene and water by dehydration reaction and then supplied; otherwise the resulting mixed gas is not sent through said dehydration catalyst and directly supplied; to an oxidation catalyst layer maintained at a predetermined temperature to obtain methacrolein and/or methacrylic acid by catalytic gas phase oxidation reaction.
As described above, t-butanol vaporized is, in many cases, used in the same way as isobutylene is used.
There are a lot of reports that the yield of methacrolein and methacrylic acid by using t-butanol as a raw material is usually the same as by using isobutylene as a raw material.
On the other hand, it is known that a dehydration reaction of t-butanol with a dehydration catalyst is an endothermic reaction, and because said endothermic reaction has adverse effects on the following oxidation reaction, several methods to avoid it have been proposed. For example, in Patent Literature 1, there is described a method to obtain methacrolein and /or methacrylic acid in a good yield, where no lower than 50% of t-butanol is decomposed into isobutylene and water by dehydration reaction with oxidation catalyst in advance and supplied to an oxidation catalyst layer. In said Patent Literature, it is specifically described that gamma-alumina-silica (γ-alumina: 90%, silica: 10%) of dehydration catalyst is charged into a gas mixer and inert α-alumina-silica is charged as a preheating layer in a reaction tube, at a length of 80 cm (whole length of the reaction tube: 2 m), to dehydrate t-butanol to isobutylene, and then the isobutylene is then turned to methacrolein and methacrylic acid by oxidation reaction.
Also in Examples 16 and 17 of Patent Literature 2, there is described an example where 20 ml of silicon carbide or α-alumina based on 3 ml of a catalyst is charged for dehydration of t-butanol to turn it to methacrolein and methacrylic acid by catalytic gas phase oxidation reaction.
Patent Literature 1: JP 63-216835 A
Patent Literature 2: JP 51-12605 B